I have a rule that goes, if I really, really thoroughly enjoy a game, then I draw a piece of fanart for it that expresses what I liked so much about it.
I'm not sure that many of you will have played Cave Story, but I am sure that you should.
It's a free platformer game that was made entirely (art, programming, music, the lot) by one guy, who then put it on the web for free. It's old school style, with fun gameplay, interesting characters and a story that is surprisingly deep.
And you can have a puppy on your head. <3
Time: ~10 hours
Tools: Photoshop CS5, Thinkpad tablet laptop & Wacom Intuous tablet